1. Field of the Invention
The present invention relates to an ink jet recording apparatus including a recording head configured to discharge ink from a plurality of discharge ports disposed on the recording head to perform recording, and a suction mechanism configured to maintain and recover an ink discharge performance of the recording head.
2. Description of the Related Art
Generally, a recording apparatus having a recording function, such as a printer, a copying machine, a facsimile machine, a word processor, a mailing machine, or a quick printing machine, records an image (also including a character, a symbol, and the like) on a recording material with a recording head based on image information. The recording apparatus can be classified into an ink jet type, a thermal transfer type, a laser beam type, a heat sensitive type, and a wire dot-matrix type based on various recording methods. Among these types, an ink jet recording apparatus is configured to discharge ink from a recording head to a recording material based on image information and to record an image on the recording material. As a recording material, a material allowing an image to be formed thereon with ink, such as a paper sheet, a plastic sheet, a photographic printing paper, a sheet for an overhead projector (OHP), a fabric, or the like, is usable.
Further, in the recording apparatus, a scanning method includes a serial type and a line type. The serial type forms an image while alternately repeating a main scan and a sub-scan. The main scan moves a recording head along a recording material. The sub-scan executes a paper delivery of a recording material at a predetermined pitch. The line type forms an image only with a paper delivery (sub-scan) of a recording material while recording one line in a lump using a full multi-head or the like.
An ink jet recording head is configured to discharge an ink droplet from a minute discharge port using an energy generating element. An ink discharge mechanism using the energy generating element includes those of discharging ink using an electromechanical converter, such as a piezoelectric element. Further, the ink discharge mechanism also includes those of discharging ink by a heating action performed when an electromagnetic wave, such as a laser, is irradiated. Furthermore, the ink discharge mechanism also includes those of discharging ink using an electrothermal converter, such as a heating resistance element. A mechanism of discharging ink by generation of heat is configured to generate film boiling of ink utilizing thermal energy and to discharge ink by the pressure of a bubble generated in ink.
In particular, a recording head which discharges ink utilizing generation of heat is advantageous in the following points. Since discharge ports can be arrayed relatively easily and in a high density, the recording head is advantageous to execute recording of high resolution. Further, since a mechanical structure of the recording head can be easily simplified, the recording head can also be easily miniaturized. Furthermore, the advantages of an integrated circuit (IC) technique and a micro-machining technique, which reflect the recent remarkable progress in technology and increase in reliability in a semiconductor field, enable high-density packaging without difficulty and a cost reduction in manufacturing the recording head.
The above-described ink jet recording apparatus discharges ink from a minute discharge port. In a minute discharge port, there may occur the mixture of bubbles and dust into the ink, or ink thickening or the like due to evaporation of an ink solvent. In such a case, ink is no longer suitable for recording, and thus the ink jet recording apparatus may have trouble performing normal image recording. In order to avoid such circumstances, the ink jet recording apparatus performs recovery processing for removing the cause of defective discharge by refreshing ink in a discharge port. As a mechanism to execute this process, the ink jet recording apparatus includes a discharge recovery unit in a position outside a recording area. An exemplary recovery unit configured to execute this recovery processing includes a cap for covering discharge ports arrayed on a discharge surface of the recording head and a suction pump connected to the cap for generating a negative pressure acting on the discharge ports.
Then, a recovery action includes a suction recovery action which applies suction force by a suction pump with the discharge ports covered with a cap to forcibly suction ink from the discharge ports. Further, the recovery action also includes a pressure recovery action which discharges ink from discharge ports while the discharge port surface faces the cap or a separately-provided ink receiver.
On the other hand, in order to prevent a rebound and a leak of ink from a discharge port at the time of a recording action or a suction recovery action, an ink absorber can be located inside the cap. Further, as a solution to when a rebound and a leak of ink occur, the ink jet recording apparatus executes a wiping action, which wipes and cleans a discharge port surface by a flexible wiper, and a preliminary discharge action, which refreshes ink by discharging color-intermingled ink immediately before the start of recording.
However, in a conventional ink jet recording apparatus, the following problem remains to be solved. That is, due to a recent advance in colorization, image quality, resolution, and processing speed of an ink jet recording apparatus, the number of types of ink, the number of discharge ports, or the number of ink colors is on the increase. Further, downsizing of a discharged ink droplet is also in progress. Thus, it is necessary to suitably maintain the property of ink to be discharged from a recording head. Consequently, it is increasingly important to securely remove bubbles or thickened ink remaining in a discharge port.
Further, the ink absorber mounted in a cap is in the form of porous matrix, in which a large pressure loss may occur during discharge and suction of ink. Accordingly, a tendency of an uneven pressure distribution inside the ink absorber causes a problem in which suction recovery in respective discharge ports cannot appropriately be performed. That is, during a suction recovery action, a large suction force is applied to a discharge port in an area adjacent to a suction hole of the cap and a small suction force is applied to a discharge port in an area apart from the suction hole. Such an unbalanced suction force distribution occurs. Therefore, it is difficult to control recovery processing of a recording head.
Further, in recent years, the ink jet recording apparatus has a tendency to miniaturize a discharge port associated with a finer liquid droplet, to increase the number of discharge port arrays associated with an increase in number of ink colors, and to increase the number of discharge ports associated with high resolution and high speed. According to these tendencies, the ink jet recording apparatus is apt to cause such disadvantages that a pressure loss of the whole discharge ports of the recording head is increased and nonuniformity of suction force acting on respective discharge ports is increased. These cause a further reduction in function of suction recovery. That is, as a difference in negative pressure distribution in a cap is made large, a suction balance to the whole discharge ports is made worse. Thus, the ink jet recording apparatus cannot efficiently suction ink from the discharge port. This causes insufficient removal of a bubble or thickened ink in a discharge port, an increase in suction amount and suction time, a decrease in recording quality, and a decrease in performance of the ink jet recording apparatus itself.
With respect to these technical problems, in a conventional technique, several methods are proposed. These methods include a method for suctioning ink with separate caps for each discharge port array of color ink, and a method for suctioning ink from discharge port arrays of respective color inks one after another with a single suction cap. However, these methods cause such disadvantages that an apparatus main body becomes complicated, an apparatus becomes large, a manufacturing cost increases, and recovery processing time becomes long.